Process of pulping raw cellulosic material



Patented Nov. 12, 1929 UNITED STATES GEORGE A. RICHTER, OE BERLIN,

PATENT? OFFICE NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPANY I OF BERLIN, NEW .EAMPSHIRE, A. CORPORATION OF MAINE PROCESS OF IPULIPING- RAW CELLULOSIG MATERIAL No Drawing. Application filed June 1,

.In the pulpmaking industry, ,the chemical pulping of raw cellulosic materials such as wood has heretofore been carried on by batch operation. For instance, it'is the usual prac- 6 ties to charge a digesterwith chipped wood and cooking liquor, and then to close the digester and to cook the charge at elevated temperature and under pressure until fiber liberation has been efl'ected. The reason for this 10 practice is apparently due to the fact that the encrusting or cementitiousv content of the wood can be dissolved by the cooking liquor only at temperatures materially above 212 F., and in order to attain such temperatures it is necessary to maintain the liquor under sufi'icient pressure to raise its boiling point to or above such temperatures. Apparently, the pressure maintained during-cooking has no function other than permitting the attainment of fiber-liberating temperatures, for if chipped wood be di ested at 212 F., for nstance in a cooking iquor such as ordinarily employed in kraft digestion, fiber liberation will not be eflected, even if a pressure in the order of magnitude of 100 pounds be mamtained during digestion.

I have discovered that rawcellulosic material such as wood may be pulped under atmospheric pressure if a cooking llquor of a composition permitting the attainment of I fiber-liberating temperatures be employed. In producing a cooking liquor of this character, I dissolve in the liquor a water-soluble or water-miscible body in amount to raise its boiling point sufficiently to permit reach ing fiber-liberating temperatures. The loodies which I employ do not undergo decomposition at such temperatures, nor do they injure the resulting pulp. Various bodies are available for this purp0se,--ethylene glycol, and/ or glycerol, or other polyhydric alcohols, for instance, being espeoiallv suitable, as they may be readily recovered from the spent cooking liquor, as by steam distillation One of the major advantages of a process such as described is that the pulping of raw cellulosic materials such as Wood may be carried out continuously in open tanks, thereby eliminat ing the necessity of expensive high pressure vnot react with the 1928. Serial no. 282,276.

digesters and the hazard incident to their operation.

While the process of the present invention may be applied when using liquors of acid, neutral, and alkaline character, it is especially applicable to quick-cooking processes where batch operation involves a greater loss of time than in slow-cooking processes. For instance, the process of the present invention .may be applied advantageously when wood is being pulped by an alkaline process of digestion such as the soda process, or the kraft process, so-called. 1 I c In preparing cooking liquors such as I employ according to the process of the present invention, the fiber-liberating chemical may be used in substantially the same amount as 1n ordinary cooking llquors, but a portion of the water usually employed is replaced by an amount of water-soluble or water-miscible body sufficient to permit the attainment of fiber-liberating temperatures under atmospheric pressure. The temperature range for fiber liberation without injuring the pulp is from about 250 to about 350 F, so that if glycerol is used for raising the boiling point of the liquor, it should be added in amount I varying from about 80% to about 96% of the weight of the water employed. One of the advantages of using lycerol, is that it does flier-liberating chemical or undergo decomposition, even when raised to its boiling point, and in no way injures the raw cellulosic material or the resulting pulp. Furthermore, a substantial propor-. tion of the spent liquor resulting from digestion may be reused, while glycerol present in the rest of the spent liquor may be readily recovered as by steam distillation. After distillation, the residual liquor is highly concentrated in spent chemical, so that recovery of the chemical therefrom may be efiected without concentrating such liquor. In other words, after glycerol has been steam-distilled from the spent liquor, the residual liquor containing the spent chemical may be introduced directly into a furnace wherein its organic content is burned and its inorganic content converted into smelted compor'ids which may 100 he dissolved in water and used for the preparaliquor was of 35% tion of fresh cooking liquor.

One procedure which gave satisfactory results in actual practice was carried out substantally as follows. White birch in the form of chips and a liquor consisting of a I111X-- 'ture of 10% water and 90% glycerol and con- The charge was gradually heated to fiber-libcrating temperatures, digestiombeing continued over a period'of about six hours between about 238 to 300 F. At the end of this-time, a good yield of pulp having about the same color, strength, and tear resistance as the usual kraft pulp was obtained.

Various liquors other than that given in the foregoing example, of greater or less alkalinity and/or sulphidity, may be employed according to the present invention, to produce pulps of various physical and chemical characteristics. So, too, other kinds of wood, such as spruce and poplar, may be employed as the raw material, and fiber liberation effected under somewhat different time and temperature conditions.

The pulp may be separated or washed free from the spent liquor of digestion. A portion of the spent liquor, sayabout 50%, may be reused together with fresh cooking liquor, and the remaining liquor subjected to steam distillation for the recovery of glycerol for reuse in the preparation of fresh cooking liquor. The spent chemical re'mains dis-' solved in the aqueous residue left in the still. This residue, being highly concentrated in chemical, may be delivered directly into a recovery furnace wherein its combustible content is burned and its inorganic content smelted to produce a smelt of the desired coma position. The smelt may be dissolved in water and-used in'the preparation of fresh cooking liquors.- 1 Having thus described certain embodiments of this invention, it is evident to those skilled in the art that various changes and modifications might be made therein without departing from the spirit or scope of invention as defined in the appended claims.

What I claim is: f 1. A process of pulping raw cellulosic material, which comprises digesting such material. under 'atmospheric pressure and at aqueous cooking liquor comprising a berliberating chemical and a water-miscible body permitting the attainment of such temperatures at such pressure.

3. A process of pulping raw cellulosic material which comprises digesting such material under atmospheric pressure and at fiber-liberating temperatures in an aqueous cooking liquor comprising fiber-liberating chemical and glycerol in. amount suflicient to permit the attainment of such temperatures at such pressure.

4. A process of pulping raw cellulosic material, which comprises digesting such material under atmospheric pressure and at fiber-liberating temperatures in a cooking liquor comprising a mixture of water and glycerol containing fiber-liberating chemical, separating the resulting pulp from the spent liquor, and recovering glycerol from suchspent liquor for the preparation of fresh cooking liquor.

5. A process of pulping raw cellulosic material, which comprises digesting such material under atmospheric pressure and at fiber-liberating temperatures in a cooking liquor comprising a mixture of water and glycerol containing inorganic fiber-liberating chemical, separating the resulting pulp from the spent liquor, and steam-distilling glycerol from such spent liquor and recovering the valuable inorganic content from the remaining aqueous liquor for the preparationof fresh cooking liquor.

6. ,A process of pulping raw cellulosic material, which comprises digesting such material under atmospheric pressure and at fiber-liberating temperatures in an alkaline cooking liquor comprising a mixture of water and glycerol having a fiber-liberating chem ical contentsubstantially similar to that of a kraft cooking liquor, separating the resulting pulp from the spent liquor, and steamdistilling glycerol from such spent liquor and smelting the valuable inorganic content of the remaining aqueous liquor for the preparation of fresh cooking liquor.

in testimony whereof I have afixed my signature.

GEQRGE A. RICHTER.

temperatures materially above 212 F. in I an aqueous cooking liquor comprising fiberliberating chemical and a water-miscible body permitting the attainment ,of such temperatures at such pressure.

. 2. A process of pulping raw cellulosic material, which comprises digesting such material under atmospheric pressure at term 

